Cystic Fibrosis (CF) is associated with several dysfunctional modes in airways in addition to the abnormal Cl- secretion which is a hallmark of the disease. These other abnormalities include enhanced Na+ reabsorption, abnormal processing and trafficking of proteins and membrane vesicles, and chronic Pseudomonas infection. The key question is how does CFTR (cystic fibrosis transmembrane conductance regulator) interact with these other processes to ensure that they function normally? This is an important question, since mortality in CF occurs from repeated lung infection brought about by viscous mucus secretions and not directly from defective Cl- channel function. It is also known that CFTR regulates outwardly rectifying Cl- channels (ORCCs) which have biophysical properties distinct from CFTR Cl- channels. During this grant period, the regulatory interaction of CFTR with ORCCs will be studied as a model to define in detail the specific mechanisms whereby CFTR can affect more than one airway epithelial cell process. In addition, the functional role of the transmembrane domains of CFTR will be explored to understand better the role of mutations in transmembrane domains in CF. The following questions will be addressed: 1. What is the mechanism of coupling between outwardly rectifying Cl- channels and CFTR in airway cells? 2. What structural domains of CFTR are critical for CFTR Cl- channel function? and finally, 3. What structural domains of CFTR are critical for the regulatory interaction between CFTR and outwardly rectifying Cl channels? Information generated from this grant may help us develop strategies for a pharmacologic therapy for CF.